1. FIELD OF THE INVENTION
The present invention relates generally to subsurface equipment for subterranean wells and, in particular, to a seal receptacle for connection in a well conduit for permitting expansion and contraction of the conduit.
2. DESCRIPTION OF THE PRIOR ART
Typically, a tubing string in a subterranean well is secured to a well casing by utilizing one or more packers or other well tools spaced at predetermined intervals along the tubing.
Well tubing is subjected to a wide range of temperature and pressure variations which may result in contraction and expansion of the tubing. Consequently, a seal receptacle assembly is connected in the well tubing to permit the tubing to expand and contract without inducing any load on the packer assembly or other well tool. Such seal receptacle assemblies typically have a lower end connected to the upper portion of the packer assembly or other well tool and an upper end connected to the lower end of the well tubing or conduit.
Prior art seal receptacle assemblies typically include an inner seal mandrel having a lower end connected to the well tool, and an outer seal housing having an upper end connected to the lower end of the well tubing or other conduit. The outer housing has an inner cylindrical polished surface in which is mounted an annular sealing element. The outer housing and the sealing element telescope over the upper portion of the seal mandrel. The seal mandrel has an outer cylindrical polished surface for sealingly and slidably engaging the sealing element. Since the polished surface on the outer housing remains static relative to the sealing element, this surface is typically referred to as the static sealing surface. The polished surface on the seal mandrel slides within the sealing element and, therefore, is typically referred to as the dynamic sealing surface.
There are several problems associated with the prior art seal receptacle assemblies. First, since the dynamic sealing surface is on the outside surface of the mandrel, it must be protected against any marring which subsequently would damage the seals. This problem leads to increased costs in both the manufacturing and handling operations of the mandrel.
Another problem occurs after the seal receptacle assembly has been down hole for some time and it is desired to replace the sealing element and redress the dynamic sealing surface. In prior art seal receptacle assemblies, this process requires two separate retrieval operations. First, the well tubing is pulled up the well conduit with the outer housing and the seal element. Next, a second retrieval operation is performed to retrieve the dynamic sealing surface on the seal mandrel. During this retrieval process, the unprotected outer dynamic sealing surface is easily damaged.